Lubricants by shakeer

TOPIC :

LUBRICANTS & MECHANISM OF LUBRICATION

Subject: APPLIED CHEMISTRY-II 2ND

SEM

1

BY :ABDUL SHAKEER

Lecturer in Chemistry

LIET

HIMAYATSAGAR

PUNJAB EDUSAT SOCIETY

LUBRICANTS

The substances which are used to

decrease the force of friction between the

moving parts of machine in contact are

known as Lubricants and the process of

decreasing the force of friction between

the moving parts of machine in contact is

known as Lubrication.

Introduction:

When on surface of machinery moves

over the another surface, resistance to

relative motion of the surfaces arises.

When we look at the solid surface it

appears smooth to naked eye , but this

smooth surface shows irregularities of

projections and cavities when viewed

under high power microscope.

PUNJAB EDUSAT SOCIETY 3

Projections and cavities in surfaces


When one such surface is placed over

another, its projections fall into the

cavities of the other and get interlocked

.Due to this interlocking , there is

resistance to the relative motion of the

surfaces. This is called the frictional

forces or frictional resistance of friction.

In due course of motion, the old

projections get broken and deformities

Friction

Friction may be defined as the

opposing force that is set up between

the surface of contact, when one body

moves over the surface of another

body.


Friction

The frictional forces oppose the relativemotion between the moving parts of amachine. Therefore extra energy has tobe spent to overcome the friction , whichincreases expenses of energy .The frictionbetween the moving parts of machinesalso produces heat which causes damageto the machinery. Thus friction causeswear and tear of the moving parts ofmachinery in contact and due to this,themachines lose their efficiency andbecome useless.


Functions of Lubricantsi) Lubricants avoid the damage of the

moving parts of machines by minimizingthe production of heat.

ii) Lubricants reduce the wear and tear ofmachinery by keeping the moving partsof machines apart.

iii) Lubricants reduce the maintenance andrunning cost of machine.

iv) Lubricants act as the coolant because itreduces the production of heat betweenthe moving parts of machine in contact.


Functions of Lubricants

V. Lubricants increases the efficiency

of machine by reducing the loss of

energy.

VI. By using the lubricants, the relative

motion of the moving parts of

machine becomes smooth and noise

level of running machine reduces.

VII. Lubricants also act as the corrosion

preventers.


VIII.Lubricants also act as a seal as in piston.

Lubricant used between piston and walls of the

container (cylinder) prevents the leakage of hot

gases produced by the internal combustion i.e.it

act as seal.


Mechanism of Lubricants

(TYPES OF LUBRICATION)

In order to lubricate a machine we have

to keep in mind the conditions under

which the machine is working.

There are 3 types of mechanisms by

which lubrication is done.


Hydrodynamic or Fluid Film or Thick Film Lubrication

Boundary Lubrication or Thin Film Lubrication

Extreme Pressure Lubrication


The 3 types are

Hydrodynamic or Fluid Film or

Thick Film Lubrication This type of lubrication is done in those

cases where liquid lubricants having

minimum viscosity under working

conditions are used and at the same

time, it should remain in place and

separate the moving or sliding parts of

the machine.


Hydrodynamic or Fluid Film or

Thick Film Lubrication


In the fluid film lubrication, the liquid lubricant fills the

grooves or irregularities of the sliding surfaces, and

forms a thick layer in between them so that there is

no direct contact between the sliding surfaces. In

this way, the lubricant reduce the wear and tear by

reducing the frictional resistance produced by the

movement of sliding parts.


Hydrodynamic or Fluid Film or Thick

Film Lubrication

The frictional resistance to the movement of

the sliding parts is only due to the internal

resistance between the particles of the

lubricant.


Hydrodynamic Lubrication

The frictional resistance is independent of

the load, But depends upon the area and

relative velocity of the sliding parts and

viscosity, thickness of the lubricants. Due

to this reason, the light machines like

watches, clocks, guns, scientific

instruments etc. and delicate machines

are provided with fluid film lubrications.


Boundary Lubrication or Thin Film

Lubrication

Where thick film lubrication fails, thin film lubrication is done .

Thin film or boundary Lubrication is done for those cases in which the continuous film of lubrication cannot persist and direct metal to metal contact is possible.


Boundary Lubrication


This happens when

i) a Shaft starts moving from rest

ii) the speed is very low

iii) load is very high and iv) viscosity

of lubricating oil is very low.


In boundary lubrication, the oily

lubricant is filled in between the sliding

or moving metallic surfaces, which is

adsorbed on both the metallic surfaces

by any physical or chemical means and

cannot be removed easily .The

adsorbed lubricant from two thin layers

between the sliding metallic surfaces

and avoid the direct metal to metal

contact. As a result of this ,the frictional

resistance between the sliding metallic

surfaces is reducedPUNJAB EDUSAT SOCIETY 20

A thin lubricant should have high

viscosity index, good resistance to heat

and oxidation, good oiliness and low

pour point.


Velocity

Vegetable and animal oils and their

soaps possess great property of

adsorption and are used for thin film

lubrication.

Graphite and molybdenum disulphide in

oil are also used for boundary

lubrication. These lubricants form a thin

film on the metallic surfaces, which

reduces the friction and can bear

compression as well as high

temperature.PUNJAB EDUSAT SOCIETY 22

For the boundary lubrication, the

lubricant molecules should possess

these properties They should have long hydrocarbon

chains and the lateral attraction

between the chains.

They should have the active polar

groups or atoms to promote spreading

and to form the linkage with the

metallic surfaces at high pressure



The fast moving or sliding metallic

surfaces under very high pressure

produce a large amount of heat and

temperature becomes very high. At

high temperature the ordinary liquid

lubricants decompose or even

vapourises at such a high temperature

and fail to stick over the metallic

surfaces .To face such conditions

Extreme pressure Additives are added

to the mineral oils. PUNJAB EDUSAT SOCIETY 24


The Extreme pressure Additives are

the organic compounds possessing

the active radicals or groups such as

chlorine, sulphur , phosphorus etc.

These compounds react with metallic

surfaces at high temperature to form

metallic chlorides,



sulphides or phosphides which can

form surface layers on the moving or

sliding metallic surfaces and act as

good lubricants.


Summary

Lubricants –Definition, Introduction

Functions of Lubricant

Mechanism of Lubricant(Types of

Lubrication)


Hydrodynamic or Fluid Film or Thick Film Lubrication

Boundary Lubrication or Thin Film Lubrication


Multiple Choice Questions A Lubricant is used with the object to

a)increase frictional heat b)increase resistance

c)decreasing frictional resistances

d)Providing direct contact between rubbing surfaces

Boundary lubrication is used for a)watches b) calculators c) light machines. d) when Load is very high

c d


MCQ

Lubricant does not act as a a) seal b)resistant c)corrosion resistant d)coolant

Which is not mechanism of lubrication a)thin film b)thick film c)temperature lubrication d) extreme pressure lubrication

Vegetable oils are used for a)thin film b)thick film c)temperature lubrication d) extreme pressure lubrication

b c a


MCQ

For Fast moving machines which produce large amount of heat, the lubricating mechanism is a)thin film b)thick film c)temperature lubrication d) extreme pressure lubrication

They should have the active polar groups. This is true for….......lubrication

a)thin film b)thick film c)Normal d) extreme pressure

d aPUNJAB EDUSAT SOCIETY 30

State True or False

The lubricants for boundary lubricants should have Long Hydrocarbon chains.

Lubricant act as a corrosion preventer.

Lubricant does not act as a seal.

Lubricants increase the efficiency of machine.

Lubricants increase the running cost of Machine.

Thick film lubricants have polar groups.


True/False

Graphite and molybdenum disulphide

in oil are used for boundary

lubrication.

Vegetable and animal oils possess

great property of adsorption.

A thick lubricant should have high

viscosity index.

A thin lubricant should have low pour

point.


Fill in the Blanks Boundary lubrication is also called……

Lubrication.

Thick film lubrication is also called……

Lubrication.

In Pistons ,Lubricant act as a ………

Lubricants increase the ……….of

machine.

Lubricant used for watches is ……….

At high temperature where normal

lubricant vaporise ……………lubricant is

used.PUNJAB EDUSAT SOCIETY 33

Thank You


Lubricants by shakeer

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